This application is for the purchase of a high-density 256 Channel Geodesic EEG System from Electrical Geodesics, Inc. (EGI). This equipment will be used as a part of the developmental neuroimaging program (DNP) of the Yale University School of Medicine that brings together a multidisciplinary group of investigators interested in basic questions of neural development in children and adults. Nine investigators from the Child Study Center, the Departments of Diagnostic Imaging and Adult Psychiatry, as well as the University of Louisville will be users of this system. An oversight committee from the DNP will regulate access to the system that will be housed in the Child Study Center. The PI has experience with the EGI system through collaboration with investigators at the University of Louisville who have extensively used high-density EEG methods. Each of the investigators who will be users of this equipment are most interested in the EGI system because of two advantages--the high-density cortical mapping that makes possible source localization and the ease with which studies may be done with infants and young children. Several of the planned studies include comparison and/or integration with fMRI. The EGI system permits dense mapping of EEG signals that are time-locked to the onset of an eliciting event--the event related-potential. Although there are a number of facilities at Yale to study event-related potentials, no system currently available at Yale affords the opportunity to obtain data from more than 64 channels. Increasing the number of channels to 256 affords the ability to map more accurately the cortical (or subcortical) source of change in signal in response to the stimulus. Also, no system at Yale currently offers a way to study infants and very young children in ways that minimize both the risk of infection and subject loss during the often-time consuming application of electrodes. The high-density system as developed by EGI affords a practically easy way to apply electrodes in a single net that makes it possible to study very young infants and children in whom fMRI studies are also less feasible because of the difficulties in helping infants and children minimize their motion during the procedure. The high-density mapping capacity is a particularly strong advantage for the EGI system. Source localization is an extremely important area of scientific interest among developmental neuroscientists and neuroimagers. While fMRI affords such a capacity, the event-related potential provides a finer grained level of temporal information (as short as one msec or less) regarding the brain s response to a stimulus and this level of temporal resolution is markedly superior to fMRI. Thus, the capacity for high-density mapping as offered by the EGI system makes possible the ability to create a dynamic neural profile of how an individual processes a given event.